Amino acids are not made during protein synthesis; rather, they are linked together to form a protein. Here's how that process works:
During protein synthesis, the amino acid sequence is determined by the mRNA sequence. The mRNA molecule is pulled through the ribosome, acting like a factory. As the mRNA's codons (sequences of three nucleotides) move through the ribosome's active site, they are matched up with specific transfer RNA (tRNA) molecules. Each tRNA is attached to a specific amino acid. The tRNA molecules act as adaptors, correctly placing each amino acid according to the mRNA code. This process adds amino acids one by one to the growing polypeptide chain, which will eventually fold into a functional protein.
The Role of mRNA and tRNA
The process of making a polypeptide chain involves several key players:
- mRNA: Messenger RNA carries the genetic code for the protein to be built.
- tRNA: Transfer RNA molecules carry specific amino acids. They match their anticodons to the codons of the mRNA.
- Ribosomes: These are the cellular machines where protein synthesis occurs. They facilitate the binding of mRNA and tRNA, and catalyze the formation of peptide bonds between the amino acids.
Step-by-Step Process
- The mRNA molecule binds to the ribosome.
- The ribosome reads the mRNA codon by codon.
- For each mRNA codon, a tRNA molecule with a matching anticodon comes along.
- The tRNA carries a specific amino acid.
- The ribosome attaches the new amino acid to the growing polypeptide chain.
- The mRNA continues to move through the ribosome, adding more amino acids to the chain until a stop codon is reached.
- The completed polypeptide chain is released, folding into the functional protein.
Key Takeaway
In summary, amino acids are not created during protein synthesis. Instead, pre-existing amino acids are joined together by the ribosome, following the instructions encoded in the mRNA. The tRNA molecules play the critical role of matching the mRNA code with the correct amino acid.
